Various magnetic resonance imaging techniques in conjunction with administration of exogenous contrast agent (CA) bolus (e.g., see references 1-8 below) have been employed in assessment of myocardial perfusion. One such magnetic resonance imaging technique is a prospectively triggered, fast, repetitive imaging with Inversion Recovery prepared Ultra fast Gradient Recalled Echo (IR-uGRE) sequences. Such an application, however, is sensitive to cardiac arrhythmias which are common, especially when cardiac disorders are present. T1-weighted images are used to monitor the contrast agent. During consecutive T1-weighted image acquisition to monitor the first-pass through of the contrast agent through the myocardium, the magnetization sampled by the IR-uGRE sequence depends upon the extent of T1 relaxation which occurs following acquisition of the image data in the previous cardiac cycle. For a constant heart rate, the extent of T1 relaxation between images is constant. During arrhythmia, however, the change in R--R interval allows a different amount of T1 relaxation to occur between images. As a consequence, the signal intensity and contrast detected as a function of time is modulated by sources other than the passage of the CA. In other words, an arrhythmia of the heart is a source other than the passage of the CA that modulates the amount of T1 relaxation. Since a relatively good time resolution is desired, especially with perfusion imaging where the brief passage of the CA through the myocardium is monitored, the problem encountered by the arrhythmias cannot be solved by retrospective gating without loss of information.
Prospectively triggered, magnetization prepared fast imaging sequences (e.g. Ultra fast gradient recalled echo, EPI, Spiral etc.) are increasingly employed for cardiac imaging. When magnetization preparation has to be repeated rapidly in consecutive acquisitions as encountered in anatomical imaging of the heart acquired with k-space segmentation or in assessment of myocardial perfusion in conjunction with administration of exogenous contrast agent (CA) bolus, the image signal intensity becomes sensitive to cardiac arrhythmias which are common especially when cardiac disorders are present. During prospectively triggered consecutive data acquisitions, the magnetization sampled depends upon the extent of T1 relaxation which occurs following acquisition of the previous imaging data. This is independent of whether the contrast is based on T1, T2 or T2*. For a constant heart rate, the extent of T1 relaxation between images is constant. During arrhythmia, however, the change in R--R interval allows a different amount of T1 relaxation to occur between images. Consequently, the signal intensity and contrast detected as a function of time is modulated.
Therefore, there is a need for a magnetic resonance imaging process for use on myocardial regions of interest in which T1 relaxation is not affected by arrhythmias of the heart. There is also a need for a process which is not dependent on former readings from the heart. Yet another need is a process for producing myocardial perfusion images which are not affected by arrhythmias of the heart. If such a process were available the images signal intensity and contrast detected would not be modulated. The result would be more accurate and consistent magnetic resonance images that could be used to provide for a more accurate representation of the perfusion of the heart under study with MRI.